Thirteen former Texas Department of Criminal Justice prison guards have been charged with racketeering and other crimes for allegedly taking bribes while on the job to smuggle cellular phones, drugs and tobacco to locked-up gang members.

They were among 32 people, including four other former guards, inmates and other civilians, accused of drug trafficking in a federal indictment unsealed Wednesday.

The indictment contends the conspiracy created a culture of corruption within the TDCJ's McConnell Unit in Beeville, where the smuggling occurred.

Arrests were made in at least 18 Texas cities, including San Antonio and Houston.

The probe began in 2009, when members of the white supremacist Aryan Circle gang were caught trying to smuggle stolen sport-utility vehicles from Corpus Christi to Mexico for a drug cartel, according to federal authorities.

That led to charges against several members of the Raza Unida gang for supporting racketeering by committing acts of violence including home invasions, shootings and conspiring to commit murder. During that investigation, the prison guards were implicated.

Authorities wouldn't go into specifics of how the guards and the two gangs are tied together, but TDCJ Inspector General Bruce Toney, whose office was involved in the operation, said gangs sometimes set aside ideological differences to do business together.

Toney said prohibited cellular phones enable inmates who are inside prison walls to direct action on the outside, as well as communicate with fellow gang members who are locked up elsewhere.

"They knew what they were doing and who they were helping," Toney said of the former guards, who were fired from the prison system before being indicted. "The offenders rely heavily on communication to carry out their criminal enterprise."

Toney said inmates know their mail and visits are monitored by authorities, and a contraband cellular phone allows them to get around such scrutiny.

Kenneth Magidson, the Houston-based U.S Attorney for the Southern District of Texas, said the guards and others were charged under a law established in 1969 to go after traditional organized crime families on the East Coast.

Magidson said the investigation took four years.

As the guards are charged federally, they don't face being sent to a state prison if convicted.